The present invention relates to a method for synthesizing indium phosphide (hereinafter abbreviated as “InP”) nanoparticles and the nanoparticles produced by the synthesis method. In particular, the present invention relates to a method for synthesizing InP nanoparticles which exhibit both excellent solution dispersibility and high photoluminescence (PL) intensity, and the nanoparticles produced by the synthesis method.
At present, various studies have been made on nano-order semiconductor fine particles. Such nano-order semiconductor fine particles are used in light-emitting diodes (LEDs), electroluminescence devices, photoelectric conversion devices, and the like.
II-VI compound semiconductors such as CdSe and CdS, and III-V compound semiconductors such as InP are used for the nano-order semiconductor fine particles.
One of the methods for synthesizing InP nanoparticles is the so-called solvothermal method, in which raw materials and an organic solvent are placed and sealed in a reaction container in an inert atmosphere, and heated by a heater to cause reaction under high temperature and high pressure. Another method for synthesizing InP nanoparticles is the so-called hot-soap method, in which a flask is heated in an oil-bath or the like while being supplied with an inert gas, and raw materials are introduced into a hot reaction solution through a syringe to cause reaction.
JP 2006-265022 A, JP 2008-44827 A, WO 07/138,851, JP 2009-19067 A, JP 2009-40633 A, JP 2008-279591 A, JP 2010-106119 A, and JP 2010-138367 A describe methods for synthesizing or producing InP nanoparticles according to the solvothermal method and the hot-soap method.
JP 2006-265022 A describes the following method for synthesizing InP fine particles.
First, 17.6 mg (60 μmol) of indium isopropoxide (In(OiPr)3) and 13.3 mg (60 μmol) of anhydrous indium chloride (InCl3) as indium (In) raw materials are mixed and dissolved in 2 g of trioctylphosphine which is a Lewis-base solvent. Then, 26.3 μl (90 μmol) of tris(trimethylsilyl)phosphine (P(TMS)3) as a phosphorus (P) raw material is added to this solution, and the solution is heated to 300° C. At this time, a change in color of the solution from yellow to dark brown is observed. By heating for 10 minutes, InP fine particles are synthesized. Thereafter, the reaction solution is allowed to spontaneously cool to room temperature, resulting in a dispersion of the InP fine particles dispersed in the TOP solvent.
JP 2008-44827 A describes the following method for producing InP nanoparticles.
First, trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP) that are coordinating organic solvents are mixed at a TOPO:TOP weight ratio of 1:9, and 10 mL of the mixture is taken into a three-necked flask. 0.6 g of indium chloride as an In raw material is introduced into the flask, and the mixture is stirred overnight at room temperature, to obtain a transparent solution (Step S1).
The transparent solution is heated to 175° C., 0.5 mg of tris(trimethylsilyl)phosphine as a P raw material is added to the heated transparent solution through a syringe, and the solution is held for 7 minutes as is. InP nanoparticles are thereby synthesized. After the solution is held for 7 minutes, the heat source is removed from the three-necked flask (Step S2).
The above-described steps are all operated under an inert atmosphere with argon.
Then, the synthesized InP nanoparticles are flocculated with methanol, subjected to centrifugal separation, followed by decantation (Step S3), and dispersed in hexane, to thereby remove impurities contained in the solution (Step S4). After these steps are repeated three times, a rotary evaporator is used to remove the hexane from the InP nanoparticles (Step 5).
In 10 mL of the reaction solution in which TOPO and TOP are mixed at a TOPO:TOP weight ratio of 1:9, the washed InP nanoparticles are dispersed (Step S6). The reaction solution in which the InP nanoparticles are dispersed is put into a three-necked flask and heated to 175° C. Then, after 60 minutes elapsed, the heat source is removed from the three-necked flask to terminate heating (Step 7).
WO 07/138,851 describes III-V semiconductor/SiO2 nanoparticles having a core made of a III-V semiconductor and a shell made of SiO2 in which a particle size of the core is in a range of 1 nm to 50 nm.
WO 07/138,851 describes the following method for producing the III-V semiconductor/SiO2 nanoparticles.
First, 0.5 g of trioctylphosphine oxide (TOPO) and 4.5 g of trioctylphosphine (TOP) are put in a three-necked flask and heated to 290° C. Rapidly poured therein is a mixture of 0.8 g of InCl3, 0.75 g of trismethylsilyl phosphine ((CH3)3Si)3P), 0.5 g of TOPO and 4.5 g of TOP. Then, the mixture is held at 270° C. for one day, and thereafter cooled to room temperature. In this state, dehydrated methanol is added dropwise to cause flocculation and precipitation, supernatant liquid is removed by centrifugal separation, and nanoparticles are obtained. At this time, an amount of dehydrated methanol is controlled, and the steps of dropwise addition of methanol, precipitation, and centrifugal separation are repeated, thereby obtaining precipitated flocculates of nanoparticles, which are further washed with pyridine to remove the TOP and TOPO from their surfaces. As a result, flocculates of InP nanoparticles with a particle size of 5.1 nm are obtained.
Thereafter, 3.7×10−3 g of tetraethoxysilane, 50 mL of 0.5 mol/L HCl, 50 mL of ethanol and 10−6 mol of the InP nanoparticle flocculates are put into a beaker, heated to 80° C. and stirred for an hour. As a result, a 10−5 M nanoparticle dispersion in which the InP particles have a particle size of 5.1 nm and their particle surfaces have been provided with SiO2 shells with a thickness of 1.2 nm is obtained.
JP 2009-19067 A describes a method for synthesizing semiconductor fine particles comprising InP.
In the method for synthesizing semiconductor fine particles comprising InP of JP 2009-19067 A, first, 200 mL of trioctylphosphine as an organic compound and 17.3 g of trioctylphosphine oxide as an organic compound are weighed in a glovebox at a dry nitrogen atmosphere. The trioctylphosphine and the trioctylphosphine oxide are then mixed and stirred for 10 minutes. The resultant stirred solution is referred to as “mixture solvent A.” Then, 9.9 g of indium trichloride as a group III metal element material and 7.3 g of tris(dimethylamino)phosphine as a group V element material of semiconductor fine particles are weighed in the glovebox, and the indium trichloride and the tris(dimethylamino)phosphine are mixed into the mixture solvent A. After mixing them, the mixture solvent A containing the indium trichloride and the tris(dimethylamino)phosphine is stirred for 10 minutes while being heated at 20° C. The stirred mixture solvent A is referred to as “raw material solution B.”
Next, the raw material solution B is placed in a reaction tank of an autoclave apparatus for supercritical synthesis in a vacuum atmosphere, heated to 350° C. over an hour with stirring, and then maintained at 350° C. for six hours to undergo a synthesis reaction. The raw material solution B which has undergone the synthesis reaction is referred to as “synthesis solution C.” Following the reaction step, the synthesis solution C is allowed to cool naturally to room temperature and thereafter recovered in a dry nitrogen atmosphere.
Subsequently, dehydrated methanol as a poor solvent is added dropwise to the synthesis solution C, causing soft flocculation and precipitation in the recovered synthesis solution C of semiconductor fine particles in which semiconductor crystals are formed of InP. The synthesis solution C is then subjected to centrifugal separation at 4,000 rpm for 10 minutes to recover the semiconductor fine particles from the synthesis solution C. The recovered semiconductor fine particles are again dissolved in dehydrated toluene used as a redispersion solvent, the semiconductor fine particles redissolved in the dehydrated toluene are softly flocculated with dehydrated methanol and precipitated, and centrifugal separation is performed at 4,000 rpm for 10 minutes to separate dehydrated toluene, thereby again recovering semiconductor fine particles containing InP. The above-described process using the dehydrated toluene and dehydrated methanol is repeated three times to purify the semiconductor fine particles, and the purified semiconductor fine particles are dissolved in dehydrated toluene to obtain a synthesis solution D. The synthesis solution D is in a state where unnecessary free matters from the surface modifier and synthesis by-products other than InP are removed, and accordingly semiconductor fine particles comprising InP (hereinafter, referred to as “InP nanoparticles”) are synthesized.
JP 2009-40633 A describes a method for producing InP nanoparticles, in which InP nanoparticles are produced according to the following steps S1 to S12.
In Step S1, 1 g of TOPO and 8.5 g of TOP serving as organic solvents, and 0.5 g of hexadecylamine (HDA) are taken into a three-necked flask such that the hexadecylamine (HDA) concentration in the organic solvents becomes 5 wt %. As an In raw material, 1 g of indium chloride (InCl3) is introduced therein (Step S2), and the mixture is stirred at 230° C. for 30 minutes to obtain a transparent solution (Step S3).
As a P raw material, 0.5 mg of tris(trimethylsilyl)phosphine is added in the heated transparent solution using a syringe (Step S4), and the transparent solution is immediately cooled to 210° C. and maintained for 10 minutes. By the above-described process, InP nanoparticles are synthesized (Step S5). Furthermore, after the solution is maintained for a predetermined period of time, a heating source is removed from the three-necked flask. These steps are carried out in a glovebox which is in an inert atmosphere with argon.
Next, 30 μL of the synthesized InP nanoparticles are taken into a sample tube, and 1 mL of hexane and 1 mL of butanol are added therein to obtain a transparent solution (Step S6). In addition, 50 μL of a hydrofluoric acid etching solution (a mixture solution of 5% hydrofluoric acid, 10% water and 85% 1-butanol) is added to the solution (Step S7), and the resulting solution is left to stand under a xenon lamp (500 W) for an hour, thereby subjecting the InP nanoparticles to a surface treatment (Step S8). These steps are carried out in the atmosphere.
Next, the sample subjected to the surface treatment is put in a round-bottomed flask, and heated on a hot plate set to a temperature of 130° C. with the pressure being reduced using a hydraulic rotary pump to remove the solvent (Step S9). After an hour elapsed, the round-bottomed flask is moved into the glovebox inside of which has been in an inert atmosphere with argon gas, and the argon gas is introduced into the flask. Hexane (dried solvent) and butanol (dried solvent) (1 mL each) are then added to obtain a solution in which the InP nanoparticles are dispersed (Step S10).
The resultant solution is put in a sample bottle, and the sample bottle is completely sealed to serve as a closed container (Step S11), in which argon gas is filled in a space where the solvent is not present. The sample bottle is irradiated with a xenon (Xe) lamp (500 W) at a light irradiation intensity of 0.3 W/cm2 for an hour (Step S12).
JP 2008-279591 A describes a method for producing nanocrystals having a three-layer structure including a nanocrystal core made of InP, a buffer layer made of Se and a shell layer made of ZnS.
JP 2008-279591 A describes the method for producing nanocrystals having a three-layer structure as detailed below.
First, 0.07 mmol of indium acetate, 0.3 mmol of oleic acid, and 10 g of octadecene are mixed and stirred until reaching a temperature of 120° C. under vacuum. Tris(trimethylsilyl)phosphine (0.05 mmol) and octadecene (1 mL) are added at 250° C. to react for 20 minutes. Thereafter, 0.1 M trioctylphosphine selenide solution (0.02 mL) is added, the mixture is maintained as is for 30 minutes, and a solution containing zinc, oleic acid and octadecene is added such that the amount of zinc added is 0.2 mmol. The mixture is then stirred for an hour to cause reaction. Subsequently, the reaction temperature is raised to 300° C., and 1 mL of 0.4 M trioctylphosphine sulfide solution is added to react for an hour. The above-described nanocrystals having a three-layer structure are thereby produced.
JP 2010-106119 A describes a semiconductor nanoparticle phosphor having two or more emitting regions each of which exhibits a different quantum effect alone and one or more barrier regions in a laminated structure in which the two or more emitting regions are separated by the one or more barrier regions, and the two or more emitting regions share the same quantum level via the one or more barrier regions.
JP 2010-106119 A describes the method for producing the semiconductor nanoparticle phosphor having a core-shell structure of InP/InGaP/InP as detailed below.
First, an InP core (first emitting region) is formed as follows.
Using a commercial solvent distillation apparatus, a first solution is synthesized by reacting indium chloride dissolved in a trioctylphosphine (TOP) solvent and trioctylphosphine oxide (TOPO) in a heating tank, and the temperature of the first solution is raised to 285° C.
Subsequently, a second solution is prepared by dissolving tris(trimethylsilyl)phosphine in a TOP solvent, the second solution is introduced to the first solution in the heating tank through a syringe, and the temperature of the solution is maintained at 285° C. Through the steps of cooling, purifying and isolating, a colloidal solution containing InP core particles is recovered. The recovered colloidal solution is stirred in a hydrofluoric acid (HF) etching solution (at a HF:pure water:n-butanol weight ratio of 1:2:17), possible deactivating factors such as defects and foreign matters on the InP core particle surfaces are removed, and thereafter the colloidal solution is washed with an organic solvent.
Next, a first InGaP shell (barrier region) is formed as follows.
The colloidal solution containing the InP core particles is again put in a heating tank, a mixture solution of indium chloride and gallium chloride (molar ratio 1:1) is added thereto, and the temperature of the solution is raised to 285° C. The second solution is introduced in the heating tank via a syringe. After being kept at 285° C., the solution in the tank is cooled, purified and isolated to recover the colloidal solution in which the GaInP shell is formed over the surface of the InP core. The recovered colloidal solution is subjected to the above-described etching treatment and thereafter washed with an organic solvent.
Lastly, a second InP shell (second emitting region) is formed as follows.
The colloidal solution containing the InP core/GaInP shell particles is once again put in a heating tank and undergoes the same processes as when forming the InP cores except that the solution is kept at 300° C. Accordingly, the colloidal solution in which the InP shell is formed over the surface of the GaInP shell is recovered. The recovered colloidal solution is subjected to the above-described etching treatment and thereafter washed with an organic solvent. The above-described semiconductor nanoparticle phosphor is thereby obtained.
In the method for producing InP nanoparticles of JP 2010-138367 A, first, in a glovebox in an argon gas atmosphere, 0.4 g of indium chloride (InCl3), 3 mL of trioctylphosphine (TOP, [CH3(CH2)7]3P) as a surfactant and 2.5 g of dodecylamine (DDA, CH3(CH2)11NH2) are put in an autoclave, and 5 mL of toluene (C6H5CH3) as a solvent and 0.5 mL of tris(dimethylamino)phosphine, (P[N(CH3)2]3) are further added.
Subsequently, the autoclave is brought into an electric furnace and kept at 75° C. for an hour, and is further heated to 180° C. to grow nanoparticles over 24 hours, thereby obtaining a nanoparticle dispersion. 10 mL of toluene and 6 mL of methanol are added to the nanoparticle dispersion, and the mixture is sufficiently stirred and then undergoes centrifugal separation for 10 minutes. Following the centrifugal separation, a clear supernatant liquid is taken out, thereby separating InP nanoparticles from by-products resulting from the reaction. Using the nanoparticle dispersion after removing the by-products, nanoparticles of different particle sizes are removed through a size-selective precipitation technique, and InP nanoparticles are obtained.
JP 2010-138367 A also discloses a method for producing semiconductor nanoparticles having a core-shell structure, in which a zinc sulfide shell is formed over an InP nanoparticle using ultraviolet irradiation.